Bird's eye view observations of the subepidermal nerve network of normal guinea pig skin.

This study was undertaken to visualize the subepidermal nerve networks immunohistochemically. Specimens were obtained from the normal skin of the back, abdomen and nose of seven adult male Hartley guinea pigs, and immersed in 1 M NaCl solution. Dermal sheets were obtained by separating the dermis and epidermis, followed by fixation in Zamboni's fixative. The dermal sheets were sectioned parallel to the separated surface. Using the immunoperoxidase technique and immunofluorescence, the sections were immunostained with primary antibodies to S 100 protein (S100), protein gene product 9.5 (PGP 9.5), neuron-specific enolase (NSE), substance P (SP) and calcitonin gene-related peptide (CGRP). In double-labeled immunofluorescence of PGP 9.5 and SP or CGRP, the sections were viewed under a confocal laser scanning microscope. In skin of the back and abdomen, networks of S100-, PGP 9.5- and NSE-positive fibers were observed, some of which showed a multicentric arrangement. The outermost structures were formed by the thickest fibers which were 5-10 micro m thick, the outer networks consisted of fibers 3-6 micro m thick, and the inner networks consisted of fibers 1-3 micro m thick. From these networks, single fibers approximately 0.5 micro m thick branched out and terminated in free endings. The SP- and the CGRP-positive substances appeared as granules on the PGP 9.5-positive fibers. These results confirm that the dermis has a three-layered sensory nerve plexus, i.e. deep, superficial and subepidermal. In the skin of the nose, however, nerve networks were made up of only thick fibers which were probably situated in the subpapillary dermis.